Question for all the technical types out there

U

unstable load

Well-Known Member
I run an electric hot water cylinder at home and it is currently on a timer switch that has it on for about 6 hours out of 24, just before and during high usage times.
The logic behind this is that it heats up what I need for when I need it and does not run unnecessarily during the night (for example) reheating water that won't be used for a while.

I have recently been told that with the specification of the insulation around the tank it does not save me anything running the timer, in fact it could be costing me more as the water would drop below the threshold of the thermo-switch and thus use more electricity to reheat than if it were "tickin over" permanently.

Suggestions please as to the most effecient way of doing this.

Solar is on the plans as soon as the piggy bank is fattened up eneough to manage it.
 
Hi, I have always been told to leave it on all the time

I am sure there are other better people on here who can give you a more scientific
answer with formulas. But I think of it like pushing a car along the road it takes more
energy to get it rolling than it does to keep it rolling.
 
OK. The underlying rules are first, rate of heat loss is equal to a constant times the temperature difference, second , heat input is equal to a constant times temperature gain. All you've done with decent insulation is reduced the value of the constant in the first equation. By all means work it through, but I think you'll find you are definitely applying the correct startegy.

Solar hot water heating is extremely effective, even in this country! By far the best are vacuum tube models as these allow a very high water temperature even on cloudy days. I had a flat panel system at my Downend house and on sunmmer days like today we had to run off water in the early afternoon to keep the tank from boiling! Make sure you change the main tank for a double coil model (one for solar and one for the gas boiler). These are much more effective than a separate solar pre heater tank. We found negligable use of gas heating of the hot water from late April to mid September. You should better that with evacuated tubes. Pays for itself in between 18 months and three years depending on the exact detail of the installation.

Chris
 
could never understand why some people advise leaving it on all the time does not make scientific sense, they must have shares in the electric companies or make money replacing burnt out immersion elements.

As Chris points out the hotter the water the faster the tank will give off energy and therefore use electricity to heat the water up again.

Best strategy would be to turn down the thermostat and perhaps reduce the 6 hours.
 
John,
The theory I was given is that if it's on all the time, the amount of energy used to maitain the temperature would/could be less than was needed to re-heat to temperature after an extended cool-down over night and during the off times.

I am trying to locate a meter that I will put on the line to measure my usage with it full on and cycling to prove one way or another.
 
If your with N-Power (and maybe some others) you can get a free energy monitor that connects to the main feed into the house and gives you a display in the house showing all sorts of usage stats. They're pretty good, and showed that we are using loads of electricity, mind you the bill told me that ! :(
 
Oh, and I'm fairly sure it'll take forever to reap the rewards of the solar install. Better off with a diesel generator running on waste chip-fat. Or just turn the boiler off, how often do you really use the hot water anyway ?
 
Thanks, all, for the help.
Down here in South Africa we have a utility that is a total monopoly and they managed to get government to OK a 100% tarriff hike over 3 years!
I know Solar will take a while to recoup the capital, but that is not only aimed at my costs, it is also my (misguided, if you look into it) offering to the Green brigades.

Sadly, the types of systems available to you guys in UK/Europe are frighteningly expensive to purchase here so I need to try to minimise my current usage as much as possible.

Thanks again for the points of view!!
 
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